The present invention relates to a probe for electrosurgical treatment of tissues, in particular by way of an endoscope. Probe electrodes of this kind are used to stanch the bleeding of tissues, for example in the gastrointestinal tract in general or in the colon.
German patent DE 4139029 A1 describes a device for the coagulation of biological tissue, to be used in an endoscope with a working channel, which comprises an electrical lead to be connected to a HF voltage source in order to supply coagulation current to the tissue from the distal end of the endoscope. An ionizable gas can be passed through the working channel from a gas reservoir. Within the path along which the gas flows before emerging from the nozzle opening, there is disposed an electrode connected to the electrical lead, the purpose of which is to ionize the gas and provide the coagulation current. When the apparatus is within a specific ignition distance from the tissue to be treated, an electrical arc passes from the electrode through the ionized gas into the tissue and raises the temperature of the tissue to the level necessary to stop the bleeding. In this design the electrode has a cylindrical shape and is disposed at the inner edge just ahead of the opening of the connecting lead.
In U.S. Pat. No. 5,207,675 an apparatus is described in which the coagulation of biological tissue is achieved by means of a biocompatible, flexible tube that can be movably inserted into an endoscope. This tube conducts argon gas from a gas reservoir to the distal end of the tube. A wire running through the tube is connected to a HF voltage source from which coagulation current is supplied. This wire terminates in a tungsten tip that serves as an electrode; positioned at the distal end of the tube, it ionizes the gas that emerges there and enables a discharge to be conducted through the gas stream into the tissue. As a result of the HF energy applied through this arc, the tissue is brought to the temperature required to stop bleeding. The electrode here has the form of a wire with a tungsten tip. As alternatives to this tip, various surgical instruments such as a gripper, a scalpel or the like can be installed.
From the publication Farin G.; Grund K. E.: Technology of Argon-Plasma-Coagulation with particular regard to endoscopic application; in: Endoscopic surgery and allied technologies; Vol. 2, 1994, No. 1, pp. 71-77, it is known that the direction and extent of this arc, i.e. its overall geometric form, is determined less by the gas current than by the electrical relationships, in particular those of the tissue to be treated. Therefore in many cases in which plasma coagulation is employed, it is extremely problematic to treat precisely the places in the tissue that need to be treated, while leaving adjacent parts of the tissue unaffected. Owing to the special requirements of endoscopic treatment, these problems are exacerbated here.
In view of the circumstances outlined above, it is impossible to predict accurately the effect of such a treatment method, because of the limited precision with which the direction of the arc (also called xe2x80x9cbeamxe2x80x9d below) can be determined. Furthermore, the extent and hence uniformity of the beam over the intended target region of the tissue to be treated is difficult to estimate, which in the end result forces the operator to position the electrode as close as possible to the target region in order to avoid missing it. But this increases the risk that the hot electrode will make contact with the tissue, with the result that the tissue will adhere to it and the source of bleeding will be torn open again.
According to the state of the art, as shown in FIG. 6, to avoid this risk appropriately shaped spacer pieces 80 made of poorly heat-conducting material, such as ceramic, have been placed onto the distal end of a tube 90. However, this also increases it the distance between a distal tip 71 of an electrode, which as indicated in FIG. 6 has the form of a helical discharge portion 70 of an electrical lead 30, and the tissue to be treated, with the disadvantages described above for the efficiency of the beam. Furthermore, the distal tip 71 fitted in the distal end of the tube 90 makes it necessary for the correspondingly shaped electrode to be centered during its insertion from the proximal end 92 of the tube 90 into the exit opening 91 of the spacer piece. Such an elaborately constructed probe is expensive and its service life is limited by the tendency of the electrodes previously employed to burn away.
The problems just described are not satisfactorily solved by any of the devices known so far.
The object of the present invention is to provide a probe for the electrosurgical treatment of tissues which can be manufactured by a simple means and which can be easily manipulated in the operation area, in particular with respect to the distance from the tissue to be treated at which the distal end must be positioned and with respect to an associated reduction of the risk of injury. At the same time, it is intended to provide a probe with an enhanced efficiency of the beam, with respect for example to ease of ignition as well as more precise aiming and greater uniformity.
According to the present invention there is provided a probe for the electrosurgical treatment of tissues comprising a tubular supply device to guide a noble gas from a noble-gas source to a distal end of the supply device; and an electrode comprising a discharge portion and an electrical lead which can conduct a HF current from a HF source to the discharge portion, the discharge portion being formed as a flat structure that is disposed in the supply device such that the noble gas can flow over a substantial portion of its surface area to conduct away heat.
As the discharge portion of the probe is constructed with a suitably large surface area, heating of the probe is avoided. The discharge portion, which is disposed at the distal end of the supply device with its flat surfaces extending in the direction of flow, is thus completely surrounded by the stream of noble gas, as a result of which heat is conducted away.
Hence, there is no longer any need for structural features designed to avoid injury caused by the hot probe electrode, such as the elaborately designed tube tip with a spacer piece, at least in the case of disposable probes. Furthermore, a special centering of the discharge portion within the exit opening of a spacer piece is no longer required, which enables this portion to be constructed more simply and cost-effectively. In addition, the dissipation of heat makes it possible to minimize the rate at which the discharge portion of the probe burns away, which increases its service life.
Because the discharge portion defines a large, flat region parallel to the direction of gas flow, turbulence in the gas flow in this region is reduced, which increases the uniformity and directional precision of the gas stream.
Preferably, the discharge portion of the probe is so constructed that it comprises at least one tip or sharp edge that faces toward the distal end.
As a result of this construction, the electromagnetic field is condensed onto the tip or sharp edge that is closest to the tissue to be treated, which increases the field strength in this region. It can thus be ensured that the beam originates from the centered tip of the discharge portion. Hence the field strength is increased and the ionization of the gas is improved, as a result of which the ignition distance between discharge portion and tissue to be treated is enlarged.
Preferably, the discharge portion comprises a lamina, with dimensions such that opposed edges of the lamina are fixedly engaged with an interior wall of the supply device surrounding the discharge portion. In this case the thin plate of which the discharge portion is composed can either be flat or, if spinning and turbulence of the gas stream are desired, it can be twisted.
This arrangement offers the advantage that the discharge portion becomes automatically centered in the supply device, which from a manufacturing point of view requires less expenditure of effort on adjustment and hence is more economical. It further ensures that the beam originates from the center of the supply device, which reduces the amount of heat transmitted to the supply device. In addition, the material for the lamina-shaped discharge portion is easy to obtain and also easy to process, e.g. by an etching method.
Preferably, the supply device, including its distal end, is made in one piece out of a plastics material. Because the spacer piece is eliminated by the design of the discharge portion described above, the supply device is made less complicated in structure and can thus be more economically manufactured.
Preferably the electrical lead comprises a wire and the discharge portion is made of sheet metal, the wire and the discharge portion being connected by spot-welding at at least one site. Connection of the wire to the lamina can be performed especially favorably by means of resistance welding, which offers additional advantages regarding manufacturing technique.
The present invention will now be described by way of example with reference to the accompanying drawings.